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Lots of "light bulb" comments. Remember that any simple electrical heating device (incandescent light bulb, hair dryer, soldering iron, heat gun, glue gun, etal) is essentially a resistor and will do the same thing as long as you don't exceed it's power-handling capability. Great job as always Will, I'm SO glad I found your YT channel!

Never saw your idea implemented before. It was good that you proved what damage can happen. Usually, you hear a laugh when the batteries spark and never hear how it can hurt your system! 👍

No kidding, you probably just saved my eyes and my life. Great video. Short to the point and extremely valuable information!

I sparked the contact between a 3000w psw inverter and 12v/100ah LifeP04 battery bank. The result was an unrecoverable BMS in the first battery in the bank! Good thing BattleBorn has a 10-year warranty. I wish I had seen this video first! Another FANTASTIC video, Will. Thanks for all you do.

All I could look at was the wrenches on the magnets above the batteries. Seriously though, love the content, it's refreshingly simply delivered and any unintentional humor only adds to the charm. Keep it up!

The first time in all my years of doing solar that this has been mentioned. Thank you sir!

I've watched countless videos related to this type of equipment but this is the first time I heard of this. Thanks!

Im glad you mentioned this as its something not a lot of people are aware of. For me, I use a lightbulb in a holder to charge as its a resistor and the bulb will dim once the capacitors are charged.

I listen to Wills videos just so i can hear him say “TITAN”! My favorite part every time!

Will, thank you for sharing this safety tip! I've seen others that have a DIY build for a 24 volt system and they never talked about this!

Thank God I saw this video before connecting my first inverter and battery together today. Thank you!

I discovered a method of precharging capacitors using no extra parts. Just the battery and the inverter. However, this method can only be used if you built your own battery from 3.2v cells. Simply attach the positive inverter cable to the positive side of the battery, then touch the negative cable to the negative post of the first cell in the series. Then touch it to the second negative post, then the third, etc. This allows you to use the battery itself to slowly ramp up the voltage, 3.2v at a time.

This video has been incredibly helpful. I blew the fuses in the exact same inverter you have used in your video by not pre-charging the capacitors and hope this fixes the issues

Great public service / safety announcement! I frequently see people doing this wrong, and it's so simple not to. Now with a short video that I can point to, if I forward it on people will actually watch it! Thanks Will! Keep doing what you love.

Thanks again Will for keeping things simple and easy to understand. Really appreciate your useful examples…..I’d be burning alot of money if not for folks like you….learning important stuff here.

That is good to know, I would have assumed big inverters would have some circuitry to prevent this but guess it's bad to assume! For a permanent setup you could probably have a resistor as part of the circuit by default and a separate switch to bypass it. I guess ideally two switches so you can still isolate the entire thing.

I used to use a incandescent test light to charge the capacitors in high power car audio systems. The benefit is the light glows dimmer and dimmer as the caps charge. The light across the inverter input will discharge too. Nice videos. Thanks.

Good to know. Inverter companies should include this information and a resistor in the packaging with their inverters. It wouldn't cost them Jack Diddly Squat and it might keep someone from damaging their eyes, batteries, or other equipment.

Used to drive a 48V EV in the 90' and the solution was to keep a 60W incandescent bulb in the battery compartment, so whenever I had disconnected the battery pack, but didn't want the bang and sparks when re-connecting, it was simply a matter of placing the center prong of the bulb on the battery terminal and the cable on the threaded part of the bulb, and when the bulb extinguished, the caps were charged so I could simply slide the cable onto the battery terminal with no fireworks. But yes, the authorised way of doing that is with a precharge resistor and a push button, and a small bulb to have an indication of when current is no longer flowing and the pre charge is complete.

This worked for me. Thank you. I damaged an inverter years ago not knowing this. You do a great service with your fine programs.

On old submarines the action of switching on those massive battery banks would sometimes release ball lightning .

By far one of your most important, accurate and useful video that I have seen since subbing. Way better than you loosing time on overpriced underperforming fraudulantly called solar generators.

Solark 8k comes with 2 resistors just for this reason to topup the capacitors initially.

I had no idea! My problem is now solved. I was about to return this brand new inverter 4000 watt. Thanks Will!!!!

Thanks Will, another informative episode. I am surprised to learn that large wattage inverters don't have a high value leakage resistor soldered across the input terminals to allow them to discharge over a few seconds once power is removed.

Many people install a switch or circuit breaker between the battery and inverter. Whenever the switch is flipped on, it will also generate a spark. I suppose we could manually pre-charge manually or install a push-button switch with resistor before flipping the switch but is there some kind of contactor, delay, relay, and/or device available off the shelf that can be installed across the breaker/switch to AUTOMATE the pre-charging? I doubt such an accessory cost much to make.

Dude, you are perfecting the perfect off grid system that can power a house out of a shed, including transportation! Wow! Using solar panels that can be downgraded to charge anything less powerful than and including a house! Shit, if you pakcage that like you have done with generators and sell it undercutting the market to get it out there would change everything! You do this and that's revolutionary. ✊🏽

Precharge resistors are good. You can use anything from 1Ω to 100Ω depending on how much current you want to flow, and how long you have to wait until charged. If you put a scope on it and record the voltage over time with different resistors, then you'll be able to show properly what resistance to use is best, and why.

I prevent sparks in the lithium battery by disabling "discharge" in the BMS. It's a straightforward solution!

Thanks Will. Pretty much found everything I need to know to build my van solar system and feel confident its safe and will perform from your videos alone. Saved me endless trawling through questionable advice on forums.

I always wondered why I would only get one spark and wondered why the spark was so big! Thanks! I've done 3500 watt magnum inverter chargers with 600ah busses and never could get around the massive spark! Unless I used the battery disconnect lol

I'm in the process of researching setting up a solar system on a small narrow boat over here in England. All the videos I've looked at and read up online I've not come across this information. Thank you very much.

good advice well done I have been in this trade over 50 years now .

i usually use a 12v 55watts halogen automotive headlight bulb. easy to find and you can see if pre-charging completed. innitialy bulb will lit ip and slowly dims while charging in progress

Awesome video as always saw your interview with Jamie, that was so stoked.

For my backup power system i built for my computer room. After i burnt up the contacts in a pair of high current relays i added a pre charger. Just using a resistor and a car horn relay. From memory the resistor im using is one of those ones designed for if you use LED replacement lights on your car to load the circuit more. The arduino i use to control it all just turns the precharger on for 5seconds before closing the main relay to the inverter.

WOW, it's amazing to me that the inverter manufacturers allow the terminals to stay hot for days. A 1k ohm (ish)resistor inside would discharge them fast enough and not waste too much power.

Thank you for this useful info. I have always wondered how to connect high voltage inverters without a spark, now I know

Thx for this info. I built a 3 battery bank about 4 years ago with a 2000 watt inverter and nobody ever mention this to me. Yes, i got some nice sparks when connecting the terminals to the inverter, but i figured it must just be a mild normal thing (not dangerous). Your $1 resister is about $10 with shipping.

Great video! Higher value resistors at lower wattage will work too. Just takes longer. Large value capacitors do definitely pack a punch.

Excellent video. I fried my inverter during hurricane Fiona (I'm in Prince Edward Island, Canada) and this would have saved me some grief. Thank you

⚠️ Question! What about the internal inverter switch.? Does the pre+charging of inverters apply to every scenario? Our communications engineer watched this video and mentioned “If inverter is OFF when connecting, where’s the load?” And “Does the inverter’s internal switch or relay, etc.. suffer from contact arcing and burning damage?” We are using 2000 and 3000 Watt Giandel and Renogy pure sine-wave inverters with our emergency vehicles (ambulances & light rescue) at 12v. Some are permanently mounted and powered from the vehicle batteries (2x 12v deep cycle marine type) Some are mounted in Pelican wheeled cases with 100ah LifePO4 batteries for portability. After showing Though this doesn’t apply to our fire apparatus as we have onboard diesel generators, if installing inverters in the vehicles that are all 24vdc, any particular advice? Thanks for a great channel with a truly outstanding comment section!

dude your videos are ALWAYS on point, to the point and incredibly clear and helpful - thanks a metric TON bro!! My new litto batts are ALMOST here and I just so HAPPENED to see someone popping a small switch and searched out what it was, i have a 10000w 24v split phase inverter!! You just saved me ruining alot of expensive stuff thanks thanks thanks!

I use a light bulb in a pig-tail socket to tune capacitors. That way, you get feed-back from the light glowing then going dim.

Does anyone know what resistor should be used with a 12v, 3000w inverter with a 12v LiFePO battery? A link to Amazon would be great, but I can't seem to find it in the description. Secondly, does anyone know the formula for calculating resistor? Thanks advance. Great content, Will!

Wow, good video. So, what happens when you turn your system off using a battery disconnect switch? Does this surge / spark happen within the disconnect switch when you power things back on?

Thank You for All that you are doing for our Planet Earth.... Peace.. Shalom.. Salam.. Namaste .. 🙏🏻 😊 ✌ ☮ ❤ 🕊

Making something as boring as a resistor, interesting! You've done it again. Thanks for the great info!

Great video. I have done exactly what you are doing using a value of 200 ohm or larger and leave it connected for a minute or so. Another thing I have done is use a tail light bulb from a car in series with the inverter and the battery. (12 volt system) I just leave it connected unitl the bulb goes out and give it a few seconds more for good luck. The bulb will be bright and slowly dim. If the bulb suddenly goes out it may have burnt out so be careful if using the bulb method.

Thank you for telling and EXPLAINING about the resistor to charge and to discharge. That was something nobody mention to me lol. Gordon.

I had seen this video, but forgot about the caps after blowing out a 30A fuse during some load testing. Putting in the new fuse was a little scary! The lesson is now welded in, so to speak. I didn't have a 10W low resistance resistor handy, so I put some clips on a 120vac 40w light blub. Works fine.

Thanks. Great advice. I just don't understand why some people give you a "dislike" (thumbs down). I found nothing inaccurate or not useful in your presentation. I suspect they're just jealous. My advice: "Damn the torpedoes, full speed ahead".

super informative and helpful!! Thanks for saving everyone's eyes and bank accounts !!

The thought of the spark when I am about to connect these terminals always gives me concern. Thanks Will.

Lucky to have a Fry's that is still stocked - many are suffering due to business changes. Good idea on using a resistor.

You can use a double sided pencil in a pinch, the graphite is a conductor and has around 20 ohms of resistance.

Hi, I dont see alot of people pre-charging inverters with 12v batterie battery banks AND 2000/3000 inverters. I found your video interesting and Im wondering if this applies to 12v or is more a concern with 24v batterie system and up? Cheers!

Love your videos. I've learned so much and I understand it. You have a way of explaining these ideas in easy to understand language. Thank you! Also...will you be evaluating the new Ecoflow Delta 1300 solar generator? That one looks promising but I would love to see what you find out about it.

It can also damage the inverter!.. I use a 60-100 watt light bulb, the incandescent bulb can glow for a few seconds, but when its charged , it will stop glowing,

Great video, thanks. What about if the inverter (connected) is turned off for extended period of time. Do the capacitors remain charged?

Had a buddy loose an eye for not prechargeing , they call him pop- eye😅😂

Chunky soft shop pencils work well too! Mine measured about 20ohms.

Just another tip when it comes to capacitors, it is really easy to calculate the resistor needed. But this only work IF you a aware of the capacitance of the bank. What you calculate is the time constant or RC R=resistor C=capacitors. t=R*C so if you got a 30ohm resistor and a bank of 100'000uF (0,1F), just put those values in the formula and BAM! 30Ohm * 0,1F = 3s to about 60% charge if they're completelly drained. The second advice is, why bother with dischargin when you easily can just permanatly mount a resistor beetween the power "poles/skrews" and as soon as you disconnect the battery bank it starts to drain the capacitors. Same formula just the opposit result. But I'd use a larger on, let's say 1K (1000Ohm) which will drain the capacitors within 2min. A 1000 ohm resistor will draw about 0,012A or 0,144W so you'll ned atleast a 1/4W or 1/2W resistor. No disessambly required at all for any of this tips.

Thanks, you are the only one on you-tube that has said to do this, I guess all those experts need to learn a little more. You would think that at least Battle Born would tell their customers that in a video??

Hi Will, Thanks for all the videos and detailed explanations. You have helped to make our RV electrical upgrade easier and safer. Thank you! Tod

It such a good point that it is very disappointing that no practical solutions are offered when for when fitting an inverter in situ - particulary as they will be turned off and back on on a regular basis - even pointing the way to some off the shelf solutions (well anything really) would have been really helpful

Thanks for the great advice and safety tips. I hope all your viewers heed your advice. Like your channel for the great information about solar products and your honest reviews of the products.

I feel safe just watching Will's videos.

If you don't have a resister you can use a light bulb.

"It will create a huge spark that don't have molten metal go right in your eye!" That's The story of My Life.

Just found your channel today. Already subscribed. You just gave me an answer to an issue I have in my RV power system. I have two Battle Born batteries wired in parallel going to a Blue Sea battery switch. I also have a Victron Energy MultiPlus Compact 12/2000 Inverter Charger. Every so often when I switch the batteries on the system would not start. I would have to cycle the switch off and back on to get it running. After watching your video, I now know that I was triggering a disconnect on the Battle Born Charge Controllers. To fix this I will get a momentary toggle SPST switch and that wire-wound resistor and put them across the switch terminals. I will toggle the switch on for a couple of seconds before switching the batteries into the system. Thank you very much.

Very useful info for DIY enthusiasts, I personally use car/mo-bike tail lamps [filament type not LED] for charge discharge those capacitors. ;)

All good Will. But spending on a 2 buck resistor is totally unnecessary on the 12V inverter level. Just tap in a 1156 ish 12v bulb or just about any 12v bulb. Dissipates that energy pronto. Whether powering up a new inverter or Dissipating the energy in an old inverter. Just wait for the light to go out😂. Job done. Let's not over think resistance

The Epever Ipower plus (5000W) has current limit to prevent sparkles/Arc when connecting the 48V batteries bank, this is nice, I did not have to use a resistor (LifePO4)

I would think an easier way to do this is install a circuit breaker somewhere, leave it open, but jump the terminals with the resistor. Once it's charged up, then flip the breaker.

All good info. I was just looking for how to safely discharge my inverter.

00:33 And that can really hurt sometimes! 😃

If you don't want to go buy a resistor, a 1 foot length of .032 stainless safety wire has about 7 ohms. It's what I use to make discharge load banks.

I always used an incandescent light bulb, when the bulb goes out, you know it's charged. It also works the same way to discharge. With a 12 or 24v system a regular automotive test light works great. Any voltage higher might be a little difficult to find a bulb for though?

Yeah, I fried my 48v inverter Growatt 6kw inverter, 4 mosfets were fried by the inrush of current, with my 35kwh lithium battery bank. Do this, save yourself the hassle and do this.

Switching on three MultiPlus-II 48/5000/70-50 in parallel with just the bms (jk bms b2a20s20p) works fine for me so far 👍

Looking dorky is being safe, thanks for the video, 👍👌❤🇨🇦

Does that only need to be done to an inverter once in its lifetime?

A friend of mine actually tested a super cap to see how fast they discharged, they did overnight !, not sure if all capacitors are like that tho.

Thanks for addressing safety issues!

I wired my resistor directly on my battery switch ....once the switch is on...the resistor is no longer in the circuit...this way I never forget. ...

Near infinitely-low impedances create near infinitely-large currents. I=V/R. With R tending to zero, I tends to infinity, regardless of the voltage. Another way to do it is use a thin wire, but wear gloves and be firesafe doing this incase of mistakes - melted plastic will stick to your hands and keep burning - very unfunny. The resistor way is best.

Great info as always! This channel is amazing.

Victron smartsolar mppt controller has no manual switch built in. So a loud pop and arc/spark occurred every time I connect it to battery. How do I stop this from happening?You present decent quality video contents. Thank you sir.

You might want to caution users regarding higher DC Voltage as there is the potential for an electrical shock that could be hazardous to health. I would be cautious with voltage greater than 48V.

The bigger issue is actually the capacitors especially on the larger inverters as I don't think I have seen any that have a soft charge up feature (like some computer power supplys have, the ones that don't spark when you plug them in do have it, they limit the power to the psu for 1-2 seconds then allow full power pass) , I have seen the solder or traces blown off around the the capacitors legs due to the very high amp inrush current At basic level I guess using thermistors to limit inrush

Thanks! Glad I saw this video before putting together a new solar system.

Is this (resistor) required if you don't disconnect the hot or ground ? Is this (resistor) only required during initial hook up of Hot and Ground to terminals ?

Wow I had no idea we had to do that great information thank you.

Great info and safety PSA also! Save your eyes!

So at least in California Fry’s electronics has now gone out of business. Just an FYI great video thanks

The eyewear does not look dorky. In fact they're pretty cool 😎

You are best video I watch 100 %

Nice video Will...safety first...